When I render something, there's an indent in the model, but when It's not rendered there is no indent. how do I fix this?
There are some problems with your topology. Also, if you want to stay low-poly without any Subdivision Surface, you have to use the Auto Smooth, otherwise the twisted planes of your object will always create artifacts.

First of all, you have unwanted faces. If you go in Edit / Face Select mode, you can see some faces squeezed between faces. It has nothing to do with the problem you're talking about but anyway you need to correct that because it's not good to keep this kind of topology. It must have been created by some accidental extrusions. So select all your vertices with A and click W > Remove Double, it will merge all overlayed vertices and remove all these unwanted faces. It's not the only problem of your topology but it's the most obvious.



Now, about your problem: Your object is made of several planes that are not flat but twisted like chips, so, as you didn't smooth your object with Smooth Shading and Subdivision Surface modifier, which would have helped to smooth these surfaces, they do appear like triangles and not like planes.

If you want to avoid these artifacts you have several solutions, you can either:


Use the Smooth Shading (in the 3D view Tool panel displayed with T > Tools tab > Edit > Shading). But it will give non very aesthetic gradients as your object doesn't have enough polygons.
Keep this Smooth Shading but add a Subdivision Surface modifier so that your object has virtually more polygons.


But these solutions are interesting only if you want to give your object a smooth and high-poly appearance. If you want to keep it low-poly you should use this trick:


Keep your object Flat and with no Subdivision Surface modifier.
Go to the Properties panel > Data > Normals and enable Auto Smooth. The Auto Smooth option is supposed to determine the angle below which the Smooth Shading will happen, but in Flat Shading it will also make your twisted plane look flat and uniform.